1.0 Field of the Invention
This invention relates generally to viscous product dispensers, and more particularly to an apparatus and a process for dosing paste-form substances and for mixing them with a solvent by an injector with an integrated shutoff member.
2.0 Discussion of Related Art
Liquid to paste-form detergents are known in large numbers. They are generally formulated to meet domestic requirements, i.e. they are expected to be sufficiently liquid so that they can be poured out and measured/dosed without difficulty. Since, in addition, they are expected to be stable in storage over a relatively broad temperature range, the use of organic solvents and/or hydrotropic additives cannot normally be avoided. However, such additives do not contribute to the actual washing process, are comparatively expensive and, in addition, take up packaging space and transportation and storage capacity. The presence of inflammable solvents is particularly troublesome and necessitates additional safety precautions because of the relatively high consumption of detergents in laundries. As a result, detergent concentrates of the type mentioned can only be used to a limited extent, if at all, in laundries.
Accordingly, powder-form detergents are mainly used in laundries. Since the exact dosing of powder-form detergents is problematical or labor-intensive, particularly in large and extensively automated laundries, the detergents are mostly stored and dispensed in predissolved form as stock liquors, i.e. a water-based concentrate is prepared and delivered to the individual points of consumption. However, the detergents typically used in laundries contain comparatively high levels of washing alkalis which are only soluble to a limited extent in cold water and, in addition, lead to so-called salting-out effects. They promote phase separation with the result that the organic components, more especially the nonionic surfactants and soaps, separate and cream up. Accordingly, the concentrates have to be diluted relatively heavily with water and, in addition, the stock liquors have to be constantly and intensively mixed and circulated to prevent individual components being deposited in the feed lines to the points of consumption. Processes such as these require considerable investment in large mixing vessels and the associated static mixers and feeders, and also a constant supply of energy for the heating and circulation of the stock liquors.
A detergent which meets these requirements is proposed in EP 0 295 525. This detergent is a paste which imposes particular demands on handling for the purpose of dosing and mixing with water as solvent. An injector operating on the principle of the water jet pump with an integrated shutoff member is proposed in this document for dosing and mixing. A measuring arrangement based on conductivity measurements is disclosed as the dose size detector. A chemical dispenser for dosing chemical solutions of unknown concentration or variable concentration in conjunction with a detector based on conductivity measurement and a corresponding process are also described in EP 0 229 038.
The hitherto proposed solutions present difficulties for the shutoff member integrated in the injector. They are concerned either with shutting off the entry of water into the paste supply line or with shutting off the supply of paste. Hitherto, there has not been a satisfactory shutoff system which provides for controlled dosing and mixing.
3.0 Summary Of The Invention
The technical problem addressed by the present invention is to further develop a known apparatus and a process for operating this apparatus in such a way that the supplies of paste-form substances and their solvents can be separately shut off so that dosing of the mixture components in accordance with the mixing ratios possible in a simple, exact and reproducible manner and with minimal outlay.
In apparatus of the type described above, this problem has been solved by the fact that the shutoff member is a dual control piston assembly for separately closing an opening between the paste supply line and an injector suction chamber, and an opening between the solvent supply line and an injector ante-chamber. In addition, the process described above which through the opening of a solvent shutoff member in a feed line for the solvent under pressure, a dual control piston assembly moves against counteracting force and, in doing so, initially opens a connection between a paste feed line and an injector suction chamber. Thereafter, a connection between a solvent feed line and an injector ante-chamber, results in paste being taken into the injector, which operates on the principle of a water jet pump. The paste is mixed with the advancing solvent and the resulting mixture is injected into a measuring zone in which the quantity of paste dissolved in the mixture is determined by a conductivity measuring arrangement and, after a preset dose size has been reached, the solvent shutoff member is closed, after which the preceding opening sequence takes place in the reverse order for shutting off.
The dosing/dispensing arrangement according to the invention has the advantage that, through the separate shutting off of the paste and solvent feed lines, controlled dosing taking the exact mixing ratios into account is possible with simple means. It is of particular advantage if, during opening, first the paste feed line and then the solvent feed line are opened and if, during shutting off, these steps take place in reverse order. This ensures that the mixing ratios remain the same over the entire dosing time.
The arrangement of the dual control piston assembly assembly in accordance with the invention on a common piston plate, include which the solvent under pressure is designed to impinge when the dosing/dispensing system is activated, enables a very simple and effective sequential control to be inexpensively obtained. The use of a 2/2 shutoff member, i.e. a switch with only two positions, namely fully open and fully closed, has the advantage that the solvent is always under the pressure favorable to the sequential switching. In conjunction with this arrangement, the determination known per se of the dose size on the basis of a conductivity measurement affords particular advantages because, together, they provide for very precise dosing.
The design of an outlet pipe for the solvent from the space in which the piston plate is accommodated as a bypass between that space and the measuring zone represents an advantageous solution which, with minimal outlay and without significantly affecting the dosing and mixing result, enables the solvent to be removed from that space so that the dual control piston assembly can be completely closed. Other solutions for removing the solvent would require very expensive 3/2 fittings in the solvent feed line and/or expensive connections to a disposal line.
The control system proposed in one particular embodiment readily enables the sequences of the individual switching steps to be effectively controlled and monitored. The proposed process or method advantageously affords the possibility of carrying out dosing and mixing by injector and dose size determination on the basis of conductivity measurement in a form which optimally utilizes the possibilities of these units and combines them with one another in a simple manner, enabling the invention to be advantageously put into practice.
The apparatus and method according to the invention are described above all with reference to paste-form detergents and their use in washing processes after dosing and mixing. In washing processes, water is usually the preferred solvent. However, they are equally suitable for other paste-form chemicals and solvents.